Microgrid electric power generation systems and associated methods

ABSTRACT

A method for operating a microgrid electric power generation system includes delivering energy to an electric power bus at least partially from one or more kinetic generators electrically coupled to the electric power bus, controlling the one or more kinetic generators in response to a change in a load such that a magnitude of a voltage on the electric power bus remains within a predetermined voltage range, and controlling one or more combustion generators electrically coupled to the electric power bus based at least in part on an operating state of the one or more kinetic generators. The one or more kinetic generators are capable of (a) delivering energy stored therein to the electric power bus, and (b) storing energy in kinetic form.

CROSS REFERENCE TO RELATED APPLICATIONS

The present application is a continuation of U.S. patent applicationSer. No. 16/060,144, with a § 371(c) date of 13 Nov. 2018, which is a 35U.S.C. § 371 filing of International Application No. PCT/DK2016/000047,filed 7 Dec. 2016, which claims priority to Danish Patent ApplicationNo. PA 2015 00789 filed 7 Dec. 2015 and International Patent ApplicationNo. PCT/DK2016/000006 filed 22 Feb. 2016, the entire contents of whichare incorporated herein by reference.

BACKGROUND

An offshore drilling rig (also referred to as mobile offshore drillingunit (MODU)) typically includes a self-contained electric power system,often referred to as a “microgrid,” to power a variety of electric loadson the drilling rig. Examples of such loads include drawworks, winches,hydraulic power units (HPUs), electric thrusters, mud pumps, top drives,rotary tables, dynamic braking systems, cement pumps, cranes andperipheral electrical loads. Some of these electric loads are relativelyconstant. For example, lighting, HVAC (heating, ventilation and airconditioning), pumps, agitators, mixers, and air compressors commonlypresent a base load of approximately one to five megawatts (MW). Mudpumps, top drives, and rotary tables may also present a relativelyconstant electric load.

On the other hand, some significant electric loads on an offshoredrilling rig may be very dynamic. For instance, drawworks, winches,thrusters, cranes and HPUs present highly variable loads with peak powerdemands that are, for example, two to three times larger than typicalbase loads. As one particular example, some drawworks have a loadrequirement that can vary by up to ten MW in less than twenty secondsand that can ramp up from zero to about seven MW in less than twoseconds. As another example, each thruster on a drilling rig mayrepresent a maximum load of around five MW, and a typical drilling rigmay have six to eight thrusters, resulting in a total thruster maximumload of over thirty MW. Each thruster may ramp up to its maximum load inapproximately ten to twenty seconds, and multiple thrusters may beactivated at once. Thrusters may therefore present a very largetransient load on a drilling rig. Consequentially, an offshore drillingrig's microgrid must support significant transient, as well assteady-state, electric loads. Additionally, an offshore drilling rig'smicrogrid must be highly reliable since an electric power failure or“blackout” may have catastrophic consequences, including loss of life,significant environmental damage, and large economic loss.

AC combustion generators or “gensets” are commonly used to provideelectric power in a microgrid. These generators require significant timeto start-up, and these generators cannot quickly respond to load changesdue to their large inertia. Consequently, these generators areconventionally operated with large “spinning reserve,” i.e., sparegenerating capacity of operating generators, to support load increases,as well as to ensure sufficient generator capacity in case of a singlegenerator failure. Supercapacitors are typically also provided tosupport transient loads, especially large load decreases. Batterystorage subsystems are sometimes provided to supply power for a limitedtime in the event of complete generator failure. Battery storagesubsystems, however, respond relatively slowing to transients loads, andtherefore, supercapacitors are needed to supplement a battery storagesystem.

SUMMARY

In an embodiment, a method for operating a microgrid electric powergeneration system includes (a) delivering energy to an electric powerbus at least partially from one or more kinetic generators electricallycoupled to the electric power bus, the one or more kinetic generatorsstoring energy therein in kinetic form; (b) controlling the one or morekinetic generators in response to a change in a load powered by theelectric power bus such that a magnitude of a voltage on the electricpower bus remains within a predetermined voltage range; and (c)controlling one or more combustion generators electrically coupled tothe electric power bus based at least in part on an operating state ofthe one or more kinetic generators.

In an embodiment, controlling the one or more combustion generatorsincludes maintaining an output power of the one or more combustiongenerators at a constant value during the change in load.

In an embodiment, the method further includes maintaining the outputpower of the one or more combustion generators at eighty percent or moreof a maximum rated output power of the one or more combustion generatorsduring the change in load.

In an embodiment, the method further includes controlling the one ormore combustion generators in response to a signal indicating anupcoming change in the load.

In an embodiment, controlling the one or more combustion generatorselectrically coupled to the electric power bus based at least in part onthe operating state of the one or more kinetic generators includescontrolling the one or more combustion generators according to one ormore of (a) kinetic energy storage level of the one or more kineticgenerators and (b) kinetic energy loss rate of the one or more kineticgenerators.

In an embodiment, the method further includes (a) controlling the one ormore kinetic generators in response to the change in the load within 10ms of the change in load and (b) controlling the one or more combustiongenerators at least one second after the change in load.

In an embodiment, the step of controlling the one or more combustiongenerators includes initiating change in operation of the one or morecombustion generators; and changing power output of the one or morecombustion generators at least one second after the step of initiating.

In an embodiment, the method further includes controlling the one ormore combustion generators without consideration of the voltage on theelectric power bus.

In an embodiment, the method further includes providing an output powerof at least 1 MW from the one or more kinetic generators to the load forat least 5 minutes.

In an embodiment, the method further includes spinning a rotor of eachkinetic generator at a speed of at least 30,000 revolutions per minute.

In an embodiment, the method further includes controlling the one ormore kinetic generators such that frequency of the voltage on theelectric power bus remains within a predetermined frequency range.

In an embodiment, a method for operating a microgrid electric powergeneration system includes (a) operating one or more combustiongenerators electrically coupled to an electric power bus such that anoutput power of the one or more combustion generators is at least 60% ofa maximum rated output power of the one or more combustion generators;and (b) in response to a change in a load powered by electric power bus,changing an output power of one or more kinetic generators electricallycoupled to the electric power bus within 2 ms of the change in load, tocompensate for the change in the load, where the one or more kineticgenerators are capable of (1) delivering energy stored therein to theload, and (2) storing energy in kinetic form. In an embodiment, themethod further includes providing an output power of at least 1 MW fromthe one or more kinetic generators to the load for at least 5 minutes.In an embodiment, the method further includes operating the one or morecombustion generators within ten percent of an optimum operating pointof a specific fuel consumption curve of the one or more combustiongenerators. The method additionally includes, in an embodiment, changingthe output power of the one or more combustion generators in response toa change in operating state of the kinetic generator. In an embodiment,the method further includes providing more power to the load from theone or more kinetic generators than from any one combustion generator ofthe one or more combustion generators.

In an embodiment, a microgrid electric power generation system includesan electric power bus, one or more combustion power sources, and one ormore kinetic energy subsystems. Each combustion power source includes(a) a combustion generator electrically coupled to the electric powerbus and (b) a first control subsystem configured to control delivery ofpower by the combustion power source to the electric power bus, whereeach combustion power source has a respective first time constantrepresenting an amount of time required for the combustion generator toa change its power output by ten percent. Each kinetic energy subsystemincludes (a) kinetic generator capable of (1) delivering energy storedtherein to the electric power bus, and (2) storing energy from theelectric power bus in kinetic form; (b) a power converter electricallycoupling the kinetic generator to the electric power bus, and (c) asecond control subsystem configured to control the kinetic generator andthe power converter of the kinetic energy subsystem such that magnitudeof a voltage on the electric power bus remains within a predeterminedvoltage range. Each kinetic energy subsystem has a respective secondtime constant representing an amount time required for the kineticenergy subsystem to change its power storage or delivery by ten percent,and each second time constant is smaller than each first time constant.

In an embodiment, each second time constant is no more than ten percentof each first time constant.

In an embodiment, each first control subsystem is further configured tocontrol its respective combustion generator based at least in part on anoperating state of the kinetic generators of the one or more kineticenergy subsystems. The operating state of the kinetic generators of theone or more kinetic energy subsystems includes at least one of (a)kinetic energy storage level of the kinetic generators and (b) kineticenergy loss rate of the kinetic generators, in a particular embodiment.

In an embodiment, the first control subsystem is further configured tocontrol its respective combustion generator without consideration of thevoltage on the electric power bus.

In an embodiment, each second control subsystem is further configured tocontrol its respective kinetic generator according to a load powered bythe electric power bus. Each second control subsystem is yet furtherconfigured to control its respective kinetic generator according to asignal indicating an upcoming change in the load powered by the electricpower bus, in a particular embodiment.

In an embodiment, each second control subsystem is further configured tocontrol its respective kinetic generator such that frequency of thevoltage on the electric power bus remains within a predeterminedfrequency range.

In an embodiment, each kinetic generator has an energy storage capacityof at least 100 kWh and a response time of no more than 2 milliseconds.In a particular embodiment, the kinetic generators of the one or morekinetic energy subsystems collectively have a maximum power output of atleast 4 MW.

In an embodiment, the kinetic generators of the one or more kineticenergy subsystems collectively have a maximum power output that is atleast as large as a maximum power output of any one combustion generatorof the one or more combustion power sources.

In an embodiment, the electric power bus is one or more of a directcurrent (DC) electric power bus and an alternating current (AC) electricpower bus.

In an embodiment, each kinetic generator has horizontal extent of lessthan 2 meters.

In an embodiment, a rotor of each kinetic generator is capable ofrotating at a speed of at least 30,000 revolutions per minute.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 illustrates one microgrid electric power generation system,according to an embodiment.

FIG. 2 illustrates a kinetic generator, according to an embodiment.

FIG. 3 illustrates a kinetic generator with a magnetically levitatingrotor, according to an embodiment.

FIGS. 4A and 4B illustrate a kinetic generator with a magneticallylevitating rotor and a generator module that implements verticallyoriented coils, according to an embodiment.

FIGS. 5A and 5B illustrate a kinetic generator with a magneticallylevitating rotor and a generator module implementing horizontallyoriented coils, according to an embodiment.

FIG. 6 is a graph of load versus time of an exemplary active heavedrawworks.

FIG. 7 is a graph of power versus time in one possible application ofthe FIG. 1 system, according to an embodiment.

FIG. 8 which is a graph of power versus time of a microgrid electricpower generation system without kinetic generators.

FIG. 9 is a graph of power versus time in another possible applicationof the FIG. 1 system, according to an embodiment.

FIG. 10 is a graph of power versus time illustrating power requirementsof one exemplary emergency shutdown scenario of a drilling rig.

FIG. 11 illustrates one microgrid electric power generation systemincluding two alternating current (AC) electric power buses, accordingto an embodiment.

FIG. 12 illustrates one microgrid electric power generation systemincluding an AC electric power bus and a direct current (DC) electricpower bus, according to an embodiment.

FIG. 13 illustrates a method for operating a microgrid electric powergeneration system, according to an embodiment.

FIG. 14 illustrates another method for operating a microgrid electricpower generation system, according to an embodiment.

DETAILED DESCRIPTION OF THE EMBODIMENTS

Applicant has developed microgrid electric power generation systems andassociated methods which significantly advance the state of the art.These electric power generation systems include one or more kineticgenerators which enable the systems to support transient loads withoutlarge generator spinning reserve, thereby promoting efficient operationand small system size. Additionally, the kinetic generators can power alarge load for a significant time in the event of generator failure,thereby reducing, or even eliminating, the need for a battery storagesubsystem to provide backup power. Reduction or elimination of a batterystorage subsystem may achieve significant system cost and size savings,as well as improve system reliability and reduce system maintenancerequirements. Furthermore, the fast response of the kinetic generatorsenables certain embodiments of the present systems to support transientloads without supercapacitors, thereby further promoting low systemcost, small system size, and high system reliability. Moreover, certainembodiments of the featured systems are capable of storing power fromregenerative braking for later use, thereby promoting efficiency andresistance to reverse power tripping.

FIG. 1 illustrates a microgrid electric power generation system 100including an AC electric power bus 102, one or more combustiongenerators 104 electrically coupled to electric power bus 102, and oneor more kinetic generators 108 electrically coupled to electric powerbus 102 via a respective power converter in the form of an AC-to-ACconverter 110. Although not required, it is anticipated that load 112,symbolically shown as a single element in FIG. 1 for illustrativeclarity, is also electrically coupled to electric power bus 102. Load112 represents electric load of one or more elements electricallycoupled to electric power bus 102 that are powered from electric powerbus 102. For example, in a drilling rig application of system 100, load112 may represent electric load of elements such as drawworks, winches,HPUs, electric thrusters, mud pumps, top drives, rotary tables, dynamicbraking systems, and peripheral electrical loads. Load 112 may includeelectric load of elements directly connected to electric power bus 102,as well electric load of elements connected to another electric powerbus, such as a DC electric power bus or another AC electric power bus,that is electrically coupled to electric power bus 102. In some cases,load 112 may be negative, such as in cases where load 112 includeselectric load of hoisting equipment or other equipment operating in aregenerative braking mode. Although FIG. 1 illustrates two instances ofcombustion generator 104 and two instances of kinetic generator 108, thenumber of each of these instances may vary without departing from thescope hereof.

Each combustion generator 104 includes a combustion engine, such as adiesel engine, mechanically driving an AC generator electrically coupledto electric power bus 102, such that each combustion generator 104 iscapable of providing electric power to electric power bus 102. In someembodiments, electric power bus 102 is a three-phase bus, and eachcombustion generator is a three-phase generator. A nominal voltageV_(bus) on electric power bus 102 is, for example, 690 volts inlow-voltage applications of system 100, and nominal voltage V_(bus) is6.6 to 11 kilovolts in certain embodiments of system 100 in high-voltageapplications of system 100. However, nominal magnitude of voltageV_(bus) may vary without departing from scope hereof. System 100optionally further includes a respective circuit breaker (not shown)electrically coupled between each combustion generator 104 and electricpower bus 102.

Kinetic generators 108 are capable of storing energy in kinetic form.Kinetic generators 108 receive energy for storage from electric powerbus 102 in an acceleration mode, where energy on electric power bus 102is provided by combustion generators 104 and/or by a regenerativebraking component of load 112. Kinetic generators 108 are additionallycapable of efficiently delivering energy stored therein back to electricpower bus 102 in a generator mode. Importantly, kinetic generators 108have a large energy storage capacity and are capable of quicklyresponding to a change in load. Kinetic generators 108 are also capableof storing and delivering energy at a high rate. In particularembodiments, each kinetic generator 108 (a) is capable of responding toa change in load within ten milliseconds, or within one millisecond insome embodiments, (b) has an energy storage capacity of at least 100kilowatt hours (kWh), and (c) has a maximum peak power output of atleast one megawatt (MW). Additionally, in some embodiments, all kineticgenerator 108 instances collectively have an energy storage capacity ofat least one megawatt hour (MWh) and are capable of providing an outputpower of at least 1 MW for five or more minutes. Additionally, incertain embodiments, kinetic generators 108 collectively have a maximumpower output that is at least as great as that of any one combustiongenerator 104 instance, such as 4-10 MW. As discussed below, thesefeatures of kinetic generators 108 help system 100 achieve significantadvantages compared to conventional microgrid electric power generatorsystems. In particular embodiments, each kinetic generator 108 hashorizontal extent of less than 2 meters, such as 1.5 meters to promotesmall system size.

FIG. 2 illustrates a kinetic generator 200, which is one exemplaryembodiment of kinetic generator 108. Kinetic generator 200 is capable of(a) converting electrical energy to kinetic energy in the form ofrotational energy at high efficiency, (b) storing the kinetic energywith low loss, and (c) converting the kinetic energy to electricalenergy at high efficiency. Kinetic generator 200 includes a rotor 210and a shaft 220. Rotor 210 is mechanically and rigidly coupled withshaft 220, and rotor 210 and shaft 220 are configured to rotate about anaxis 290 in a direction 292. Direction 292 may be opposite that shown inFIG. 2 without departing from the scope hereof. FIG. 2 shows kineticgenerator 200 in cross-sectional view, with the cross section includingaxis 290.

Kinetic generator 200 is configured to be coupled to an electric bus 282via kinetic electronic circuitry 280. Kinetic electronic circuitry 280encompasses, for example, an instance of AC-to-AC converter 110 and aninstance of second control subsystem 120 (discussed below). Bus 282 is,for example, electric power bus 102 of FIG. 1. Kinetic generator 200generates and delivers electrical energy to bus 282 via kineticelectronic circuitry 280, or receives electrical energy from bus 282 viakinetic electronic circuitry 280. Kinetic electronic circuitry 280controls whether kinetic generator 200 is operating in generator mode,acceleration mode, or passive storage mode. In generator mode, kineticgenerator 200 converts kinetic energy stored in the rotation of rotor210 to electrical energy to be delivered to bus 282. In accelerationmode, kinetic generator 200 uses electrical energy received from bus 282to accelerate the rotation of rotor 210 about axis 290. In passivestorage mode, kinetic generator 200 neither receives nor generateselectrical energy. The direction 292 of rotation about axis 290 is thesame in generator mode, acceleration mode, and passive storage mode.Kinetic generator 200 may switch between any two of these modes with aresponse time of less than 25 milliseconds, such as in the range between0.1 and 50.0 milliseconds or in the range between 0.1 and 1.0milliseconds. In one exemplary scenario, kinetic electronic circuitry280 switches the operation mode of kinetic generator 200 fromacceleration mode or passive storage mode to a maximum power output ofthe generator mode within the response time stated above. These fastresponse times allow kinetic generator 200 to respond to changes in loadat a time scale much faster than that achievable by a combustiongenerator. Thus, kinetic generator 200 is capable of performing peakshaving and, for example, remove voltage drops caused by increases inpower demand at a time scale of about a millisecond or a fraction of amillisecond. For comparison, the response time of a combustion generatoris on the order of seconds or more, and the response time of a batteryis on the order of about 100 milliseconds or more. Supercapacitors arecapable of responding with a time scale of the order of milliseconds.However, the energy capacity of a conventional supercapacitor, or even aconventional supercapacitor array, is orders of magnitude lower than theenergy capacity of kinetic generator 200.

In one example, the maximum power output of kinetic generator 200 is inthe range between 0.5 and 1.5 megawatt (MW), such as approximately 1.0MW.

In certain embodiments, rotor 210 has height 212 and a cylindrical outercircumference with diameter 214. Height 212 is no greater than 3 meters,for example in the range between 1.0 and 2.5 meters such as around 1.8meters, in some embodiments. Diameter 214 is no greater than 2.5 meters,for example in the range between 1.0 and 2.0 meters such as around 1.5meters, in some embodiments. The weight of rotor 210 is no greater than2000 kilograms (kg), for example in the range between 1000 and 1500 kgsuch as around 1250 kg, in particular embodiments. Rotor 210 may besubstantially composed of a carbon composite.

Kinetic generator 200 is capable of achieving a high rotational speed.In an embodiment, rotor 210 may achieve a rotational speed of at least15,000 revolutions per minute (rpm) about axis 290, for exampleapproximately 50,000 rpm or between 30,000 rpm and at least 60,000 rpm.This high rotational speed enables high energy capacity of kineticgenerator 200. In one embodiment, the energy capacity of kineticgenerator 200 is in the range between 50 and 200 kilowatt-hours (kWh).Kinetic generator 200 is therefore capable of generating electricalenergy at a significant rate for longer periods of time. As a result,kinetic generator 200 is capable of providing electric power at a shortresponse time (as discussed above) and at a high power output and alsogenerate power over a longer period of time (such as seconds, minutes,or longer). Kinetic generator 200 thus provides, in one device, (a) thepower output and response time similar to that achievable by asupercapacitor array or a conventional flywheel and (b) longer termpower generation similar to that of a battery or battery array. Due torelatively low energy capacity, supercapacitors and conventionalflywheels are generally not capable of generating energy over a longerperiod of time (such as seconds or minutes). Furthermore, asupercapacitor array capable of producing several MW of output powerwould have physical dimensions that significantly exceed thosecharacteristic of kinetic generator 200 (e.g., height 212 and diameter214). Likewise, a battery or battery array capable of matching theenergy capacity of kinetic generator 200 will have physical dimensionsgreatly exceeding those of kinetic generator 200. A conventionalflywheel scaled up to achieve the energy capacity of kinetic generator200 would require a flywheel with physical dimensions greatly exceedingthose of rotor 210. These dimensions are not practical forimplementation onboard an offshore drilling vessel or other maritimevessel, due to the limited space onboard such vessels. In addition, aconventional flywheel scaled up in size to achieve the energy capacityof kinetic generator 200 would be orders of magnitude more expensivethan kinetic generator 200.

In one implementation, the energy capacity of kinetic generator 200 isapproximately 100 kWh. This implementation facilitates a power output ofapproximately 1 MW, which matches the power rating of certain standardelectrical components that may be used to interface kinetic generator200 with electric power bus 102. In another implementation, the energycapacity of kinetic generator 200 is less than 100 kWh, such as in therange between 10 kWh and 25 kWh. In this implementation, kineticgenerator 200 may serve to power a single machine onboard an offshoredrilling vessel.

In yet another implementation, several kinetic generators 200 cooperateto achieve a combined energy capacity of up to at least 2,000 kWh. Forexample, four kinetic generators 200 may have a combined energy capacityof at least 200 kWh or at least 400 kWh and a maximum power output of atleast 2 MW or at least 4 MW, respectively. For such kinetic generators200 may be implemented onboard a jackup offshore drilling rig. Inanother example, which may be implemented onboard a semi-submersibleoffshore drilling rig, twelve kinetic generators 200 cooperate toprovide a combined energy capacity of at least 600 kWh or at least 1200kWh and a maximum power output of at least 6 MW or at least 12 MW,respectively. A semi-submersible offshore drilling rig typically relieson dynamic positioning to maintain its position relative to the well andtherefore present greater energy demands than a typical jackup offshoredrilling rig. In a further example, sixteen kinetic generators 200cooperate to provide a combined energy capacity of at least 800 kWh orat least 1600 kWh and a maximum power output of at least 8 MW or atleast 16 MW, respectively. Such a set of sixteen kinetic generators 200may advantageously be implemented onboard a drillship having evengreater energy demands than that typically associated with asemi-submersible offshore drilling rig. It is understood that theseimplementations and examples are non-limiting and that a differentnumber of kinetic generators 200 may be implemented together to achievea wide range of energy capacities and maximum power outputs.

In one exemplary scenario of kinetic generator 200 operating ingenerator mode for a sustained period of time, kinetic generator 200generates 1 MW for up to approximately 2-3 minutes. In another exemplaryuse scenario, kinetic generator 200 performs peak shaving to ensurestable voltage on bus 282. Kinetic generator 200 is capable ofsimultaneously (a) performing peak shaving, and (b) operating ingenerator mode for a sustained period of time, for example to handle apower demand otherwise requiring a combustion generator.

Kinetic generator 200 is capable of achieving the above stated responsetimes, power outputs, and energy capacities in a relatively small andlightweight package (as stated above). The lightweight package ensurescompatibility of kinetic generator 200 with operation onboard anoffshore drilling vessel. Operation onboard an offshore drilling vessel(or other maritime vessel) is associated with spatial constraints and,due to movement of the vessel, imposes challenging demands on thestructural integrity and stability of kinetic generator 200. Kineticgenerator 200 achieves the above stated performance parameters, at leastin part, by being efficient. This high efficiency is facilitated byminimized air drag and minimized friction between mechanical componentsduring rotation of rotor 210 and shaft 220, even when kinetic generator200 is located onboard an offshore drilling vessel and subject to themovements characteristic of that environment.

For the purpose of minimizing air drag on rotor 210, kinetic generator200 includes a sealed vacuum enclosure 270 that contains rotor 210 andshaft 220 in a vacuum environment. Vacuum enclosure 270 also eliminatesexposure to oxygen and moisture, which extends the life of the internalcomponents of kinetic generator 200.

For the purpose of reducing mechanical friction between rotating andstationary parts, kinetic generator 200 is configured with low-frictionbearings. Kinetic generator 200 includes a lower bearing system 240, andan upper bearing system 250. Bearing systems 240 and 250 cooperate tosupport rotor 210 relative to vacuum enclosure 270 via shaft 220.Kinetic generator 200 is configured for rotation about a mostly verticalorientation of axis 290, that is, for rotation about axis 290 mostlyparallel to the direction of gravity. It is understood that, onboard anoffshore drilling vessel, the orientation of axis 290 may varysignificantly. Kinetic generator 200 is configured to achieve the abovestated performance parameters in the presence of movement typical ofthat associated with an offshore drilling vessel. However, the averageorientation of axis 290 is assumed to be approximately parallel to thedirection of gravity, at least to within approximately 15 degrees. Lowerbearing system 240 supports the weight of rotor 210 via shaft 220. Lowerand upper bearing systems 240 and 250 cooperate to stabilize theposition of shaft 220 in dimensions orthogonal to axis 290.

Kinetic generator 200 further includes a generator module 235 having atleast two coils 230 and at least two permanent magnets 232. Generatormodule 235 converts electrical energy to rotational energy of rotor 210or generates electrical energy from the rotational energy of rotor 210,depending on the operating mode of kinetic generator 200. Magnets 232may include or be composed of a ferromagnetic material. Magnets 232 aremechanically and rigidly coupled with rotor 210, either directly asshown in FIG. 2 and/or indirectly via shaft 220. Coils 230 aremechanically and rigidly coupled with vacuum enclosure 270 and furtherelectrically couple with kinetic electronic circuitry 280 via one ormore connectors 260. During rotation of rotor 210 about axis 290,magnets 232 pass by coils 230 and magnetically coupled therewith. Bothcoils 230 and magnets 232 are arranged at different locations alongdirection 292. Magnets 232 generate magnetic fields that aresubstantially orthogonal to direction 292, or at least predominantlyorthogonal to direction 292.

In one embodiment, generator module 235 includes one magnet 232 for eachcoil 230 to form a series of magnets 232 along direction 292 about axis290. In an example of this embodiment, magnets 232 are equidistantlyspaced along direction 292 and coils 230 are equidistantly spaced alongdirection 292. In another embodiment, kinetic generator 200 includes apair of magnets 232 for each coil 230. In this embodiment, the magnets232 of each pair of magnets 232 are placed on opposite sides of thetravel path of coils 230 during rotation of rotor 210 when viewed fromthe rest frame of rotor 210. Each pair of magnets 232 forms a magneticfield between the two magnets 232 of the pair. In an example of thisembodiment, pairs of magnets 232 are equidistantly spaced alongdirection 292, and coils 230 are equidistantly spaced along direction292.

In generator mode, magnets 232 rotate with rotor 210 about axis 290 andinduce a current in coils 230. This current is delivered to bus 282 viakinetic electronic circuitry 280. During generator mode, the rotationspeed of rotor 210 decreases as the kinetic energy of rotor 210 isconverted to electrical energy. In one example of generator mode,kinetic electronic circuitry 280 is configured to convert AC electricalenergy thus generated by kinetic generator 200 to AC electrical energyof a different frequency than that resulting from the rate of magnets232 passing by coils 230, such as for compatibility with electric powerbus 102. In another example of generator mode, kinetic electroniccircuitry 280 is configured to convert AC electrical energy thusgenerated by kinetic generator 200 to DC electrical energy, such as foruse in the system of FIG. 12 discussed below.

In acceleration mode, kinetic electronic circuitry 280 passes currentthrough coils 230. This current magnetically couples with the magneticfields generated by magnets 232 to move rotor 210 toward a preferredposition (the polar aligned position) of magnets 232 relative to coils230. Thus, coils 230 apply a torque to rotor 210 to increase therotation speed of rotor 210. As a result, the amount of kinetic energycarried by rotor 210 increases. Kinetic electronic circuitry 280actively switches the direction of current through coils 230 shortlybefore magnets 232 reach the preferred position relative to coils 230.Due to this active switching of the current direction through coils 230,the previously favored position of magnets 232 relative to coils 230becomes the least favored position. Consequently, magnets 232 forcerotor 210 to continue rotating along direction 292 past the previouslypreferred position to a new preferred position. Continued switching bykinetic electronic circuitry 280 results in continued acceleration ofrotor 210 until a maximum rotational speed is reached or until kineticgenerator 200 switches to generator mode or passive storage mode.Rotation of rotor 210 at maximum rotational speed corresponds to kineticgenerator 200 achieving its full energy capacity. Exemplary values forthe full energy capacity of kinetic generator 200 are discussed above.

In an embodiment, when viewing the series of coils 230 and the series ofmagnets 232 (or pairs of magnets 232) along direction 292, magnets 232(or pairs of magnets 232) are arranged to generate magnetic fields ofalternating direction and coils 230 have alternating polarity. In thisembodiment, any single coil 230 will, during rotation of rotor 210,experience magnetic fields generated by magnets 232 of alternatingdirection (see exemplary illustrations in FIGS. 4B and 5A). When kineticelectronic circuitry 280 actively switches the current direction throughcoils 230 during acceleration mode just prior to reaching alignment withone coil 230, the new preferred position after active switching, iswhere each magnet 232 (or pair of magnets 232) is aligned with asubsequent coil 230 along direction 292.

Generator module 235 may include one or more sensors 238. Each sensor238 is for example a Hall sensor. Each sensor 238 communicates amagnetic flux value (or associated parameter) to kinetic electroniccircuitry 280. The data received from sensor 238 indicates the positionsof coils 230 relative to magnets 232. Kinetic electronic circuitry 280may use the data received from sensor(s) 238 to determine when to switchthe direction of current through coils 230, so as to optimize theefficiency of conversion of electrical energy to kinetic energy.

In certain embodiments, coils 230 have no ferromagnetic core. Suchabsence of ferromagnetic cores eliminates hysteresis losses otherwiseincurred when magnets 232 pass by coils 230 during rotation of rotor 210about axis 290. The absence of ferromagnetic cores therefore helpsreduce loss of rotational energy of rotor 210, especially during passivestorage mode.

Without departing from the scope hereof, rotor 210 may be separated byshaft 220 at least for some portions of height 212, so as to center theweight of rotor 210 at greater radii. For example, kinetic generator 200may include a hub that affixes rotor 210 to shaft 220.

FIG. 3 illustrates one exemplary kinetic generator 300 with amagnetically levitating rotor 210. FIG. 3 shows kinetic generator 300 incross-sectional view, with the cross section including axis 290. Kineticgenerator 300 is an embodiment of kinetic generator 200. Kineticgenerator 300 implements vacuum enclosure 270 as a vacuum enclosure 370having (a) a bottom plate 372 that contacts a shaft 320 via one set ofbearings and (b) a top plate 374 that contacts shaft 320 via another setof bearings. Shaft 320 is an embodiment of shaft 220. Kinetic generator300 includes one or more permanent magnets 342 mechanically coupled withbottom plate 372, and one or more permanent magnets 344 mechanicallycoupled with shaft 320 (or, alternatively, rotor 210). Magnets 342 repelmagnets 344 to support the weight of rotor 210, shaft 320, and otherelements attached to rotor 210 and/or shaft 320, through magneticlevitation. Kinetic generator 300 also includes a magnetic bearingsystem 340 to stabilize the position of shaft 320 relative to bottomplate 372 in dimensions orthogonal to axis 290. Permanent magnets 342and 344 and magnetic bearing system 340 together form an embodiment oflower bearing system 240. Additionally, kinetic generator 300 includes amagnetic bearing system 350 to stabilize the position of shaft 320relative to top plate 374 in dimensions orthogonal to axis 290. Magneticbearing systems 340 and 350 secure and stabilize shaft 220 and rotor 210in the presence of the movement experienced onboard an offshore drillingvessel. Magnetic bearing systems 340 and 350 ensure continued operationof kinetic generator 300 in the offshore vessel environment, as well asminimize wear of kinetic generator 300 and prevent damage to kineticgenerator 300. In one implementation, each of magnetic bearing systems340 and 350 includes permanent magnets mounted to both shaft 220 and therespective one of bottom plate 372 and top plate 374. These permanentmagnets may be configured to stabilize the position of shaft 220relative to the respective one of bottom plate 372 and top plate 374 viarepulsive or attractive magnetic forces. One or both of magnetic bearingsystems 340 and 350 may include a combination of different types ofbearings.

FIGS. 4A and 4B illustrate one exemplary kinetic generator 400 with amagnetically levitating rotor 210 and a generator module 435 thatimplements coils 230 as vertically oriented coils 430. FIG. 4A showskinetic generator 400 in cross-sectional view, with the cross sectionincluding axis 290. FIG. 4B shows generator module 435 in across-sectional view that is orthogonal to that of FIG. 4A and thatincludes line 4B-4B′ shown in FIG. 4A. FIGS. 4A and 4B are best viewedtogether.

Kinetic generator 400 is an embodiment of kinetic generator 300, whichimplements generator module 235 as generator module 435. Generatormodule 435, in turn, implements coils 230 as vertically oriented coils430 coupled to top plate 374 via couplers 462. Couplers 462 mechanicallyand electrically connect coils 430 to top plate 374 and connectors 260,respectively. Without departing from the scope hereof, couplers 462 maybe integrated in top plate 374. Each coil 430 is located on a virtualcylinder surface 490, and the current running through each coil 430 hascomponents parallel to axis 290 and components parallel to direction292. For example, the current through a coil 430 may run upwards in adirection parallel to axis 290, then in a direction parallel todirection 292, then downwards in a direction parallel to axis 290, thenin a direction antiparallel to direction 292 to form a closed loop.Generator module 435 includes (a) a plurality of outer permanent magnets432 mounted to rotor 210, and (b) a plurality of inner permanent magnets434 mounted to shaft 320. When viewed from the rest frame of rotor 210,the path traveled by coils 430 (during rotation of rotor 210 about axis290) passes between outer magnets 432 and inner magnets 434.

FIG. 4B shows an example of generator module 435 that includes two outermagnets 432, two inner magnets 434, and two coils 430. Without departingfrom the scope hereof, generator module 435 may be extended to include alarger number of outer magnets 432, inner magnets 434, and coils 430, aslong as the number of outer magnets 432 equals that of inner magnets 434and the number of outer magnets 432 equals that of coils 430. Each outermagnet 432 faces a corresponding inner magnet 434 to form magnetic fieldlines therebetween. As a result, each pair of an outer magnet 432 and acorresponding inner magnet 434 forms a magnetic field that each coil 430passes through during rotation of rotor 210 (as viewed from the restframe of rotor 210). When viewed along direction 292, the direction ofthe magnetic field between corresponding magnets 432 and 434 alternates.For example, in the example shown in FIG. 4B, the magnetic field betweenouter magnet 432(1) and inner magnet 434(1) points away from axis 290,while the magnetic field between outer magnet 432(2) and inner magnet434(2) points toward axis 290. In certain embodiments, the magneticfield lines formed by outer magnets 432 and inner magnets 434 formclosed loops running in a direction through inner magnet 434(1) to outermagnet 432(1) to outer magnet 432(2) to inner magnet 434(2) and back toinner magnet 434(1) (or the opposite direction to what is describedhere). The closed loops of field lines may be substantially confined toa plane orthogonal to axis 290. In an embodiment, when viewing theseries of coils 430 along direction 292, coils 430 have alternatingpolarity.

Although not shown in FIGS. 4A and 4B, generator module 435 may includesensor(s) 238 as discussed above in reference to FIG. 2.

FIGS. 5A and 5B illustrate one exemplary kinetic generator 500 with amagnetically levitating rotor 210 and a generator module 535 thatimplements coils 230 as horizontally oriented coils 530. FIG. 5A showskinetic generator 500 in cross-sectional view, with the cross sectionincluding axis 290. FIG. 5B shows a portion of generator module 535 in aprojection view along axis 290. FIGS. 5A and 5B are best viewedtogether.

Kinetic generator 500 is an embodiment of kinetic generator 300, whichimplements generator module 235 as generator module 535. In turn,generator module 535 implements coils 230 as horizontally oriented coils530 coupled to top plate 374 via couplers 562. Couplers 562 mechanicallyand electrically connect coils 530 to top plate 374 and connectors 260,respectively. Without departing from the scope hereof, couplers 562 maybe integrated in top plate 374. Generator module 535 includes (a) aplurality of upper permanent magnets 532 mounted to shaft 320 via anupper disc 522, and (b) a plurality of lower permanent magnets 534mounted to shaft 320 via a lower disc 524. When viewed from the restframe of rotor 210, the path traveled by coils 530 (during rotation ofrotor 210 about axis 290) passes between upper magnets 532 and lowermagnets 534. Upper disc 522 and lower disc 524 may be ferromagnetic tohelp guide magnetic fields generated by magnets 532 and 534.

FIG. 5B illustrates an example of generator module 535 that includes twoupper magnets 532, two lower magnets 534, and two coils 530. Withoutdeparting from the scope hereof, generator module 535 may be extended toinclude a larger number of upper magnets 532, lower magnets 534, andcoils 530, as long as the number of upper magnets 532 equals that oflower magnets 534 and the number of upper magnets 532 equals that ofcoils 530. Each upper magnet 532 faces a corresponding lower magnet 534to form magnetic field lines therebetween. As a result, each pair of anupper magnet 532 and a corresponding lower magnet 534 forms a magneticfield that each coils 530 passes through during rotation of rotor 210(as viewed from the rest frame of rotor 210). Along direction 292, thedirection of the magnetic field between corresponding magnets 532 and534 alternates. For example, in the example shown in FIG. 5B, themagnetic field between upper magnet 532(1) and lower magnet 534(1)points in one direction parallel to axis 290, while the magnetic fieldbetween upper magnet 532(2) and lower magnet 534(2) points in theopposite direction parallel to axis 290. In certain embodiments, themagnetic field lines formed by upper magnets 532 and lower magnets 534form closed loops running in a direction through upper magnet 532(1)through lower magnet 534(1), through lower disc 524, across shaft 320,through lower disc 524, through lower magnet 534(2), to upper magnet532(2), through upper disc 522, across shaft 320, and through upper disc522 to upper magnet 532(1) (or the opposite direction to what isdescribed here). The closed loops of field lines may be substantiallyconfined to planes parallel to axis 290 and orthogonal to direction 292.In an embodiment, when viewing the series of coils 530 along direction292, coils 530 have alternating polarity.

Although not shown in FIGS. 5A and 5B, generator module 535 may includesensor(s) 238 as discussed above in reference to FIG. 2.

Returning to FIG. 1, AC-to-AC converters 110 are, for example,bidirectional switching power converters capable of transferringelectric power between their respective kinetic generators 108 andelectric power bus 102. In certain embodiments, AC-to-AC converters 110convert magnitude of voltage outputted by their respective kineticgenerator 108 to a magnitude compatible with electric power bus 102,when kinetic generators 108 are operating in generator mode. On theother hand, when kinetic generators 108 are operating in accelerationmode, AC-to-AC converters 110 convert magnitude of voltage V_(bus) onelectric power bus 102 to a magnitude compatible with kinetic generators108. In some embodiments, each AC-to-AC converter 110 includes two ormore power stages, such as two H-bridge power stages, to realizebidirectional power transfer. System 100 optionally further includes arespective circuit breaker (not shown) electrically coupled between eachkinetic generator 108 and electric power bus 102.

System 100 additionally includes a respective first control subsystem118 for each combustion generator 104, a respective second controlsubsystem 120 for each kinetic generator 108, and a power managementsubsystem 122, for controlling system 100. Each first control subsystem118 and its respective combustion generator 104 collectively form acombustion power source 124. Each first control subsystem 118 isconfigured to control delivery of power by its respective combustiongenerator 104 to electric power bus 102.

In a particular embodiment, each first control subsystem 118 includes anautomatic voltage regulator (AVR) and a governor to control itsrespective combustion generator 104. The AVR is configured to controlcurrent to field windings of the AC generator, and the governor isconfigured to control fuel to the combustion engine. In someembodiments, each first control subsystem 118 controls power delivery ofits respective combustion generator 104 to electric power bus 102 atleast partially based on a first control signal 130 from powermanagement subsystem 122. First control signal 130 represents, forexample, an operating state of kinetic generators 108, such as kineticenergy storage level of kinetic generators 108, kinetic energy loss rateof the kinetic generators 108, and/or whether kinetic generators 108 areoperating in generator or acceleration mode.

In some embodiments, kinetic generators 108 have sufficiently largecapacity and respond quickly enough to load changes such that there isno need for combustion generators 104 to regulate voltage V_(bus) onelectric power bus 102. In these embodiments, each first controlsubsystem 118 optionally controls power delivery of its respectivecombustion generator 104 to electric power bus 102 independent ofvoltage V_(bus) on electric power bus 102, or in other words, withoutconsideration of voltage V_(bus) on electric power bus 102. In someother embodiments, each first control subsystem 118 controls powerdelivery of its respective combustion generator 104 to electric powerbus 102 based at least in part on magnitude and/or frequency of voltageV_(bus), to promote tight regulation of voltage V_(bus). Even in theseembodiments, however, it is anticipated that first control subsystems118 will frequently not need to vary operation of their respectivecombustion generators 104 in response to transient load events becauseof the fast response and large energy storage capacity of kineticgenerators 108.

First control subsystems 118 optionally further promote equal sharing ofload 112 among combustion generator 104 instances by implementing one ormore of “droop” or “isochronous” (ISO) control schemes. Droop control ischaracterized by decreasing combustion engine speed with increasingmagnitude of load 112, while ISO control is characterized by maintainingconstant combustion engine speed across an expected range of load 112magnitude.

Additionally, in some embodiments, each first control subsystem 118 isconfigured to control power output of its respective combustiongenerator 104 based at least in part on magnitude of load 112. Forinstance, in a particular embodiment, each first control subsystem 118is configured to control power output of its respective combustiongenerator 104 based in part on a signal 132 representing magnitude ofload 112 to achieve “feed forward” control, to improve regulation ofvoltage V_(bus). In particular embodiments, signal 132 alternately oradditionally represents an upcoming change in magnitude of load 112,thereby enabling each first control subsystem 118 to control itsrespective kinetic generator 108 to adjust its energy storage ordelivery rate in anticipation of an upcoming load change.

Combustion generators 104 have significant inertia and are thereforeinherently incapable of quickly responding to transient loads.Consequently, each combustion power source 124 has a respective timeconstant, i.e., a time required for the combustion power source tochange its power output by at least ten percent, that is relativelylarge. In certain embodiments, each combustion power source 124 has atime constant of at least 100 milliseconds, one second, one minute, tenminutes, one hour, two hours, or one day. This time constant imposes acorresponding delay between (a) initiating a change in the operation ofa combustion generator 104 and (b) the actual power output of combustiongenerator 104 beginning to change (for example by a measurable amountsuch as 5% in power output). Thus, in certain embodiments, it takes 100milliseconds, one second, one minute, ten minutes, one hour, two hours,or one day from initiating a change in the operation of combustiongenerator 104 until the power output of combustion generator 104exhibits a significant change. In addition, there is a delay between thepower output of combustion generator 104 beginning to change and thecombustion generator 104 reaching the desired power output.

Each second control subsystem 120 is configured to control the AC-to-ACconverter 110 of its respective kinetic generator 108 and amotor/generator within the kinetic generator to control storage anddelivery of energy of the kinetic generator. In particular, inacceleration mode of kinetic generators 108, each second controlsubsystem 120 controls the AC-to-AC converter 110 of its respectivekinetic generator 108 and the motor/generator within the kineticgenerator such that energy from electric power bus 102 is stored askinetic energy in the kinetic generator. In generator mode of kineticgenerators 108, each first control subsystem 118 controls the AC-to-ACconverter 110 of its respective kinetic generator 108 and themotor/generator within the kinetic generator such that energy from thekinetic generator is delivered to electric power bus 102. Each secondcontrol subsystem 120 also controls its respective AC-to-AC converter110 in generator mode of kinetic generators 108 such that output voltageof the AC-to-AC converter at electric power bus 102 is within apredetermined voltage range and a predetermined frequency range, therebyregulating voltage V_(bus). In some embodiments, the predeterminedvoltage range is within +/−99%, 95%, or 90% of a nominal magnitude ofvoltage V_(bus). In certain embodiments, the predetermined frequencyrange is within +/−99%, 95%, or 90% of a nominal frequency of voltageV_(bus).

Each kinetic generator 108, its respective AC-to-AC converter 110, andits respective second control subsystem 120 may be collectively referredto as a kinetic energy subsystem 134. Power management subsystem 122provides a second control signal 136 to each kinetic energy subsystem134 specifying whether the kinetic energy subsystem 134 is to operate inacceleration mode or in generator mode. Each kinetic energy subsystem134 operates in either acceleration mode or generator mode according tothe state of signal 136.

Importantly, each kinetic energy subsystem 134 has a small timeconstant, i.e., time required for the kinetic energy subsystem 134 tochange its power storage or power delivery by ten percent. For example,in a particular embodiment, each kinetic energy subsystem 134 has timeconstant of 10 milliseconds or less, such that the kinetic energysubsystem 134 is capable of changing its energy storage or delivery rateby 10% within 10 milliseconds of a change in magnitude of load 112. Inanother particular embodiment, each kinetic energy subsystem 134 hastime constant of one millisecond or less, such that the kinetic energysubsystem 134 is capable of changing its energy storage or delivery rateby 10% within one millisecond of a change in magnitude of load 112. Inanother embodiment, each kinetic energy subsystem 134 has time constantof two milliseconds or less, such that the kinetic energy subsystem 134is capable of changing its energy storage or delivery rate by 10% withintwo milliseconds of a change in magnitude of load 112. In yet anotherembodiment, each kinetic energy subsystem 134 has time constant of 300milliseconds or less, such that the kinetic energy subsystem 134 iscapable of changing its energy storage or delivery rate by 10% within300 milliseconds of a change in magnitude of load 112. Such small timeconstant of kinetic energy subsystem 134 is achieved, in part, by use ofkinetic generators 108 as energy delivery devices. If kinetic energysubsystems 134 instead relied on battery storage subsystems for energydelivery, it would be impossible to achieve the small time constant ofkinetic energy subsystem 134 because a conventional battery storagesubsystem cannot respond to a transient load nearly as quickly askinetic generators 108. In some embodiments, the time constant of eachkinetic energy subsystem 134 is no more than ten percent of the timeconstant of each combustion power source 124.

In some embodiments, each second control subsystem 120 is furtherconfigured to control the AC-to-AC converter 110 of its respectivekinetic generator 108 and the motor/generator within the kineticgenerator according to signal 132 representing magnitude of load 112,thereby achieving feed forward control, which promotes tight regulationof voltage V_(bus). For example, in a particular embodiment, each secondcontrol subsystem 120 increases delivery of power by its respectivekinetic generator 108 to electric power bus 102 in response to signal132 indicating an increase in magnitude of load 112, and each secondcontrol subsystem 120 decreases delivery of power by its respectivekinetic generator 108 to electric power bus 102 in response to signal132 indicating a decrease in magnitude of load 112. In particularembodiments, signal 132 alternately or additionally represents anupcoming change in magnitude of load 112, thereby enabling each secondcontrol subsystem 120 to control its respective kinetic generator 108 toadjust its energy storage or delivery rate in anticipation of anupcoming load change.

In certain embodiments, each second control subsystem 120 changesoperation in response to a change in load only if the change in loadmeets a predetermined criteria, such as the change in load having atleast a minimum magnitude, transition time, and/or duration. Forexample, in a particular embodiment, each second control subsystem 120changes operation in response to a change in load only if the loadchange meets the following criteria: (a) the load change magnitude is atleast 1%, 5%, or 10% of the magnitude of the load before the change, (b)the load transition is less than 100 milliseconds or less than 500milliseconds, and/or (c) the load change duration is at least 500microseconds or at least 1 millisecond.

Power management subsystem 122 controls whether kinetic generators 108operate in acceleration mode or generator mode, for example, dependingon steady-state magnitude of load 112 compared to spinning reserve ofcombustion generators 104. For example, in one embodiment, powermanagement subsystem 122 causes kinetic generators 108 to switch fromacceleration mode to generator mode via second control signal 136 inresponse to magnitude of load 112 being greater than a first percentageof the spinning reserve, and power management subsystem 122 causeskinetic generators 108 to switch from generator mode to accelerationmode via second control signal 136 in response to magnitude of load 112being less than a second percentage of the spinning reserve. Inparticular embodiments, power management subsystem 122 controls poweroutput of combustion generators 104 via first control signal 130depending on whether kinetic generators 108 are operating inacceleration or generator mode. For example, in some embodiments, powermanagement subsystem 122 causes combustion generators 104 to increasetheir power output in response to kinetic generators 108 operating inacceleration mode for more than a predetermined amount of time. In someembodiments, power management subsystem 122 also generates magnitude ofsignal 132 representing magnitude of load 112, such from measurements ofvoltage V_(bus) and magnitude of current to load 112.

In certain embodiments, power management subsystem 122 includes aprocessor (not shown) communicatively coupled to a memory (not shown),and power management subsystem 122 executes instructions in the form offirmware or software stored in the memory, to achieve the functions ofpower management subsystem 122. In some other embodiments, the processorand memory are replaced by, or supplemented with, other digitalelectrical circuitry and/or analog electrical circuitry.

System 100 may achieve significant advantages relative to conventionalmicrogrid electric power generation systems. For example, the small timeconstant of kinetic energy subsystems 134 enables the kinetic energysubsystems to quickly respond to changes in load 112, thereby reducingor eliminating the need for supercapacitors in system 100. The abilityof system 100 to support transient loads may be particularly significantin offshore drilling rig applications, which as discussed above, presentsignificant transient loads. For example, FIG. 6 is a graph 600 of loadversus time of an exemplary active heave drawworks (AHDW) showing howload can vary substantially in a matter of seconds. In certainembodiments, kinetic generators 108 are able to support such dynamicload, thereby promoting high performance of the drawworks, tightregulation of voltage V_(bus) on electric power bus 102, and stableoperation of combustion generators 104. Conventional systems, incontrast, may not be fully able to support the transient of load of FIG.6, resulting in voltage distortion on an electric power bus and impairedoperation of drawworks powered from the electric power bus.

Additionally, the large energy storage capacity of kinetic generators108 and their ability to deliver energy to electric power bus 102 at ahigh rate may enable combustion generators 104 to operate with minimalspinning reserve. For example, FIG. 7 is a graph 700 of power versustime in one possible application of system 100. Curve 702 representsmagnitude of load 112, and curve 704 represents output of combustiongenerators 104. During time period t₁, magnitude of load 112 is lessthan output of combustion generators 104, and combustion generators 104are operating with a relatively small average spinning reserve 706.During time period t₂, in contrast, magnitude of load 112 is greaterthan output of combustion generators 104, and combustion generators 104therefore cannot fully support load 112 during time period t₂. However,kinetic generators 108 provide energy 708 to load 112 during time periodt₂, and load 112 is therefore satisfied even though combustiongenerators 104 cannot fully support the load. Such ability of kineticgenerators 108 to support load 112 during time period t₂ enablescombustion generators 104 to operate with small spinning reserve,thereby enabling combustion generators 104 to operate at significantcapacity, or even at near full capacity. Operating combustion generators104 at near full capacity promotes high efficiency because combustiongenerators generally operate most efficiently when near full capacity.If kinetic generators 108 were not present, spinning reserve 706 wouldneed to be larger to fully support load 112 during time period t₂.Accordingly, in a particular embodiment, combustion generators 104 arenominally operated at at least 55%, 60%, or even 80% of nominalcapacity, to promote efficient operation. Furthermore, in someembodiments, combustion generators 104 are operated close to an optimumpoint of a specific fuel oil consumption (SFOC) curve of the combustiongenerators, such as within 10% or 15% of the optimum point, to promoteefficient combustion generator 104 operation.

Furthermore, the large energy storage capacity of kinetic generators 108and their ability to deliver energy to electric power bus 102 at a highrate may enable combustion generators 104 to operate with relativelyconstant load, thereby promoting efficient combustion generator 104operation and minimal starting and stopping of combustion generators104. To help appreciate these advantages, first consider FIG. 8 which isa graph 800 of power versus time of one possible application of a systemlike system 100 of FIG. 1, but with kinetic generators 108 omitted.Curve 802 represents magnitude of load 112 as presented to combustiongenerators 104, curve 804 represents output of one combustion generator104 instance, and curve 806 represents collective output of twocombustion generator 104 instances. As can be observed from graph 800,magnitude of load 112 fluctuates between a level that can be supportedby a single operating combustion generator 104 instance and a level thatrequires two operating combustion generator 104 instances for support.Consequently, the second combustion generator instance 104 willperiodically start and stop to track magnitude of load 112, therebyresulting in inefficient operation of the second combustion generator104 instance, as well as significant wear and tear on the secondcombustion generator 104 instance.

Now consider FIG. 9, which is a graph 900 like that of FIG. 8, but withkinetic generators 108 present such that curve 902 represents magnitudeof load 112 presented to combustion generators 104 after kineticgenerators 108 support transient portions of load 112. As evident fromFIG. 9, kinetic generators 108 largely handle the transient portion ofload 112 in this particular example, such that combustion generators 104are presented with a relatively constant load that can be handled by asingle operating combustion generator 104 instance, thereby eliminatingthe need for starting and stopping of a second combustion generator 104instance.

Moreover, the large energy storage capacity of kinetic generators 108and their ability to deliver energy to electric power bus 102 at a highrate may enable system 100 to supply backup power, such as to powercritical loads and/or to provide power to facilitate quick restart ofthe combustion generators 104, in case of failure or shutdown ofcombustion generators 104. Thus, kinetic generators 108 may reduce oreliminate the need for a battery storage subsystem to provide backuppower. Additionally, the large energy storage capacity of kineticgenerators 108 and their ability to deliver energy to electric power bus102 at a high rate may enable system 100 to provide power for anemergency shutdown (ESD) in a drilling rig application of system 100.ESD in a drilling rig includes shutdown of all combustion generators,e.g., combustion generators 104, continuing operation to bring the rigto safe position, and removing the rig from a well. FIG. 10 is a graph1000 of power versus time illustrating power requirements of oneexemplary ESD scenario. During approximately the first five minutes ofthe ESD procedure, the load is approximately 12 MW and largely resultsfrom drill floor and thrusting operation. Load during approximately thenext five minutes of the ESD procedure is a little over 6 MW andprimarily results from thrusting operation. Kinetic generators 108 cansupport the load of FIG. 10 in certain embodiments of system 100,thereby facilitating ESD in drilling rig applications of system 100.

As one possible operating scenario of system 100, assume that twoinstances of combustion generators 104 are operating at eighty percentof their maximum capacity and the remaining instances of combustiongenerators 104 are not operating. Now assume that magnitude of load 112suddenly increases by thirty percent. Combustion power sources 124cannot quickly respond to this load increase due to their large timeconstants, and combustion generators 104 therefore continue to operateat eighty percent of their maximum power output during the load changeand immediately after the load change. Kinetic energy subsystems 134,however, can respond to the load increase very quickly, i.e., withinless than ten milliseconds or within less one millisecond, as discussedabove. Consequently, kinetic energy subsystems 134 increase their powerdelivery to electric power bus 102 to compensate for the thirty percentload increase within ten milliseconds, thereby minimize change involtage V_(bus) from the load change. At least 100 milliseconds afterthe load increase, or in some embodiments at least one second after theload increase, combustion power sources 124 increase their power outputby thirty percent to compensate for the load increase, thereby relievingkinetic energy subsystems 134 from supplying the increased load.

The microgrid electric power generation systems of the presentApplication are not limited to the electrical topology of system 100 ofFIG. 1. For example, FIG. 11 illustrates a microgrid electric powergeneration system 1100 including an AC first electric power bus 1102electrically coupled to an AC second electric power bus 1103 by athree-phase transformer 1105. One or more combustion generators 104 areelectrically coupled to first electric power bus 1102, and one or morekinetic generators 108 are electrically coupled to second electric powerbus 1103 via respective AC-to-AC converters 110. A first load 1112represents electric load of one or more elements powered by firstelectric power bus 1102, and a second load 1113 represents electric loadof one or more elements powered by second electric power bus 1103. In aparticular embodiment for use in an offshore drilling rig, first load1112 includes, in part, electric load of multiple drilling motors andsecond load 1113 includes, in part, electric load of multiple thrustermotors. System 1100 operates in a manner similar to that discussed abovewith respect to system 100 of FIG. 1.

System 1100 could have additional instances of combustion generators 104and/or kinetic generators 108 without departing from the scope hereof.For example, one alternate embodiment of system 1100 further includes akinetic generator 108 electrically coupled to first electric power bus1102, as well as a kinetic generator 108 electrically coupled to secondelectric power bus 1103. Furthermore, system 1100 could be modified toinclude additional AC electric power buses, as well as one or more DCelectric power buses, without departing from the scope hereof.

FIG. 12 illustrates another possible topology of a microgrid electricpower generation system including kinetic generators. In particular,FIG. 12 illustrates a microgrid electric power generation system 1200including an AC electric power bus 1202 electrically coupled to a DCelectric power bus 1203 by a three-phase transformer 1205 and anAC-to-DC converter 1207. One or more combustion generators 104 areelectrically coupled to AC electric power bus 1202, and one or morekinetic generators 108 are electrically coupled to DC electric power bus1203 via respective DC-to-AC converters 1210. Although not required, itis anticipated that a first load 1212 is powered by the AC electricpower bus 1202 and that a second load 1213 is powered by DC electricpower bus 1203. While each of first load 1212 and second load 1213 issymbolically shown as a single element in FIG. 12 for illustrativeclarity, is anticipated that each of first load 1212 and second load1213 will typically include an electric load of a number of elements. Incertain embodiments, nominal voltage of DC electric power bus 1203ranges from 720 volts to 1 kilovolt DC, and nominal voltage on ACelectric bus 1202 ranges from 6.6 to 11 kilovolts AC. However, nominalmagnitude of voltage on AC electric power bus 1202 and nominal magnitudeof voltage on DC electric power bus 1203 may vary without departing fromscope hereof.

DC-to-AC converters 1210 operate in a manner similar to AC-to-ACconverters 110 of FIG. 1, but DC-to-AC converters 1210 insteadelectrically couple a respective kinetic generator 108 to a DC electricpower bus, instead of to an AC electric power bus. In particular, inacceleration mode of kinetic generators 108, each second controlsubsystem 120 controls the DC-to-AC converter 1210 of its respectivekinetic generator 108 and the motor/generator within the kineticgenerator such that energy from DC electric power bus 1203 is stored askinetic energy in the kinetic generator. In generator mode of kineticgenerators 108, each second control subsystem 120 controls the DC-to-ACconverter 1210 of its respective kinetic generator 108 and themotor/generator within the kinetic generator such that energy from thekinetic generator is delivered to DC electric power bus 1203. Eachsecond control subsystem 120 also controls its respective DC-to-ACconverter 1210 in generator mode of kinetic generators 108 such thatoutput voltage of the DC-to-AC converter at DC electric power bus 1203is within a predetermined voltage range, thereby regulating voltageV_(bus)_dc on DC electric power bus 1203.

Each kinetic generator 108, its respective DC-to-AC converter 1210, andits respective second control subsystem 120 may be collectively referredto as a kinetic energy subsystem 1234. Similar to kinetic energysubsystem 134 of FIG. 1, each kinetic energy subsystem 1234 has a smalltime constant, i.e., time required for the kinetic energy subsystem 1234to change its power storage or delivery by 10%. For example, in aparticular embodiment, each kinetic energy subsystem 1234 has timeconstant of 10 milliseconds or less, such that the kinetic energysubsystem 1234 is capable of changing its energy storage or deliveryrate by 10% within 10 milliseconds of a change in magnitude of load 112.Accordingly, system 1200 of FIG. 12 operates in a manner similar to thatof system 100 of FIG. 1.

System 1200 could have additional instances of combustion generators 104and/or kinetic generators 108 without departing from the scope hereof.For example, one or more kinetic generators 108 could be electricallycoupled to AC electric power bus 1202 to enable one or more kineticgenerators 108 to support loads 1212 in embodiments where AC-to-DCconverter 1207 is incapable of transferring power from DC electric powerbus 1203 to AC electric power bus 1202. Furthermore, system 1200 couldbe modified to include additional AC and/or DC electric power buseswithout departing from the scope hereof.

In some embodiments of system 1200, AC-to-DC converter 1207 hasbidirectional power transfer capability. In these embodiments, system1200 is optionally configured such that kinetic generators 108 may beused to power AC electric power bus 1202 in case of failure or shutdownof combustion generators 104 through a “reverse” energy travel paththrough AC-to-DC converter 1207 and three-phase transformer 1205. Insome other embodiments, AC-to-DC converter 1207 is a unidirectionalpower converter, i.e., it can transfer power solely from AC electric bus1202 to DC electric bus 1203. In these embodiments, three-phasetransformer 1205 optionally has an auxiliary winding, in addition toprimary and secondary windings, and system 1200 further includes aDC-to-AC converter (not shown) capable of transferring power from DCelectric bus 1203 to AC electric bus 1202 via the DC-to-AC converter andthe auxiliary winding.

FIG. 13 illustrates a method 1300 for operating a microgrid electricpower generation system. In step 1302, energy is delivered to anelectric power bus from one or more kinetic generators electricallycoupled to the electric power bus. In one example of step 1302, kineticgenerators 108 deliver energy to electric power bus 102 (FIG. 1), and inanother example of step 1302, kinetic generators 108 deliver energy toDC electric power bus 1203 (FIG. 12). In step 1304, the one or morekinetic generators are controlled in response to a change in a loadelectrically coupled to the electric power bus such that a magnitude ofa voltage on the electric power bus remains within a predeterminedvoltage range. In some embodiments, the predetermined voltage range is+/−99%, 95%, or 90% of a nominal magnitude of the voltage on theelectric power bus. Additionally, in certain embodiments, step 1304 isperformed only if the change in load meets a predetermined criteria,such as the change in load having at least a minimum magnitude,transition time, and/or duration. For example, in a particularembodiment, step 1304 is performed only if the load change meets thefollowing criteria: (a) the load change magnitude is at least 1%, 5%, or10% of the magnitude of the load before the change, (b) the loadtransition is less than 100 milliseconds or less than 500 milliseconds,and/or (c) the load change duration is at least 500 microseconds or atleast 1 second. In one example of step 1304, second control subsystems120 control kinetic generators 108 such that voltage V_(bus) on electricpower bus 102 remains within a predetermined range in response to achange in magnitude of load 112 (FIG. 1). In another example of step1304, second control subsystems 120 control kinetic generators 108 suchthat voltage V_(bus)_dc on DC electric power bus 1203 remains within apredetermined range in response to a change in magnitude of load 1213(FIG. 12).

In step 1306, one or more combustion generators electrically coupled tothe electric power bus are controlled based at least in part on anoperating state of the one or more kinetic generators. In one example ofstep 1306, first control subsystems 118 control combustion generators104 based at least in part on an operating state of kinetic generators108 (FIGS. 1 and 12).

FIG. 14 illustrates a method 1400 for operating a microgrid electricpower generation system. In step 1402, one or more combustion generatorselectrically coupled to an electric power bus are operated at eightypercent or more of their maximum rated output power. In one example ofstep 1402, combustion generators 104 are operated at eighty percent ofmore of their maximum power output (FIGS. 1 and 12). In step 1404, anoutput power of one or more electric kinetic generators electricallycoupled to the electric power bus is changed within ten milliseconds inresponse to a change in a load electrically coupled to the electricpower bus. In one example of step 1404, output power of kineticgenerators 108 is changed within ten milliseconds in response to achange in magnitude of load 112 (FIG. 1), and in another example of step1404, output power of kinetic generators 108 is changed within tenmilliseconds in response to a change in magnitude of load 1212 or 1213(FIG. 12).

The previously discussed peak power demands of a drilling rig existduring certain activities or operations on the drilling rig. Theseactivities or operations includes a so-called “tripping” of the pipe ordrill stem in/out of the well, running and retrieving the riser, liftingoperations on the drill floor, lifting operations with cranes or otherhoisting equipment etc. Base load demand will vary based on theparticular well, depth of drilling, and material being drilled andequipment used for drilling operations. During oil/gas well drillingactivities, the most intermittent load is often the lifting device forthe drill floor (i.e. the lifting device for lifting tubulars in and outof the well center and to/into the seabed also referred to as thehoisting system) such as drawworks, winch, and HPU for liftingcylinders. This intermittent load causes a peak power demand during theraising or lowering of the drill pipe upwardly and downwardly in thewell. This peak power demand can be incurred by loads 2-3 times (ormore) larger than the base loads of the other demands on the drillingrig. For example, during a drilling operation it may be necessary toretrieve the drill string after finishing a section of the well or toreplace the drill bit. This drill string can be 10,000 feet or more.During the tripping in, and particularly when tripping out, of the hole,the driller (operator) demands extreme power consumption in power burstsas the driller raises (or lowers) the string of drill pipe. Since thereis a limitation on the height of the drilling mast, the operator mustlift the string out in sections (typically in stands of 2 to 4 drillpipes) by lifting a section over the drill floor, stop lifting, breakout a stand and rack it back and commence lifting again. This process isreversed during the reinsertion of the drill pipe back into the hole.This process is often referred to as “tripping” in or out of the hole.In some embodiments, the intermittent peak power demand for exampleoccurs when this load (e.g. 300,000 pounds or more) is applied to theelectric motor or motors lifting the pipe string over and over again.The load is variable since the weight of the drill stem becomes less andless as pipe sections are removed. The base load requirements for adrilling rig are approximately 1-5 MW or even higher. The peak demandcan be more than 3-9 MW or more larger than the base load. Anotherexample of intermittent loads occur when multiple machines are caused tobegin operating simultaneously. Such events may be more likely indrilling rigs with advanced automation systems so that a singleactuation by the operator can coordinate several machines to beginworking towards a particular operation.

To deliver such power bursts without overloading the activeengines/generators or requiring an excessive number of simultaneouslyactive engines/generators it is advantageous to deliver power or energyfor these power bursts by an energy storage via a DC bus or a DC bussubsection of the energy generation. This delivery of power from anenergy storage to handle temporary increases in load is often referredto as “peak-shaving.” Kinetic generators 108 of certain embodiments ofthe featured microgrid electric power generation systems are used, forexample, to deliver energy for such peak-shaving.

The featured microgrid electric power generation systems are typicallysuitable for peak shaving because kinetic generators 108 will typicallybe able to react much faster, i.e. possess a smaller time constant thanan AC generator, such as combustion generators 104, in response to peaksor bursts in the power consumption of the AC bus load or loads. In someembodiments, kinetic generators 108 have a response time 50% or lessthan that of that of the combustion generators 104, such as 25% or less,such as 10% or less, such as 5% or less such as 1% or less. In oneembodiment the response time is measured as the time to increase thepower output with 1 MW. Typically, kinetic generator 108's powerdelivery will be limited by power electronics and thus multiple kineticgenerators may be required to deliver high peaks (e.g. 6 MW for 1 or 2seconds). Some of multiple kinetic generators 108 may be connecteddirectly to separate sections of a DC electric power bus.

The energy storage capacity of kinetic generators 108 may besufficiently large, such as 360 MJ or more, such as 500 MJ or more, suchas 1200 MJ or more to power large loads on an AC electric power bus fora certain period of time. In one embodiment, kinetic generators 108 areconfigured to power a 5 MW thruster of the drilling rig for at least 5minutes during a failure of a combustion generator that would have leftthe AC electric power bus powerless. Another embodiment of kineticgenerator 108 is configured to power a 6.5 MW thruster for at least 5minutes with a 50% load. Additionally, some embodiments of kineticgenerators 108 may be capable of providing sufficient energy to drivefirst and second thrusters, e.g. each representing a load of 4-6 MW, to50% of their respective maximum power for at least 5 minutes. In someembodiments, kinetic generator 108, including the associated powerelectronics connecting the kinetic generator to an electric power bus,may be capable of providing peak power delivery larger than 2.0 MW. Asingle kinetic generator 108 or multiple kinetic generators may beconnected to the same section of the DC electric power bus.

The skilled person will understand that the microgrid electric powergeneration systems disclosed herein may include a plurality ofindividual kinetic generators 108, for example more than 2, 4, or 15individual kinetic generators. An exemplary embodiment of the microgridelectric power generation system includes 18 individual kineticgenerators each possessing an energy storage capacity of 360 MJ toprovide a total energy storage capacity of at least 6480 MJ for thesystem. The 18 individual kinetic generators may possess a combined peakpower supply capability of 6 MW or even larger.

In some embodiments, one or more of first control subsystems 118, secondcontrol subsystems 120, and power management subsystem 122 may representdetected AC voltage on an AC electric power bus in a variety of formatssuch as RMS voltage, peak voltage, instantaneous voltage, averagevoltage etc. Some parameters of the AC bus may relate to a duration of acertain AC voltage value or other waveform shape or waveformcharacteristics of the AC voltage on the AC bus. Other parameters of theAC bus may relate to an AC current or AC power flowing through the ACbus. The one or more parameters of the AC bus may characterize theelectrical integrity of the AC bus.

In certain embodiments, one or more DC electric power bus loads mayinclude at least one of: a lifting device for the drill floor, a mudpump motor, a cement pump motor, a rotary table motor. The liftingdevice may include a hoisting system for example a hoisting system witha lifting capacity larger than 500 tons or larger than 800 tons orlarger than 1000 tons or larger than 1200 tons such as larger than 1500tons.

Some embodiments of the featured microgrid electric power generationsystems may possess a multi-segmented topology including a plurality ofconnectable AC electric power bus subsections and a plurality ofconnectable DC electric power bus subsections. Hence, the AC electricpower bus may include a plurality of AC electric power bus subsectionswherein each AC electric power bus subsection includes first and secondbus tie breakers for selectively connecting and disconnecting the ACelectric power bus subsection to the AC bus; and the DC bus may includea plurality of DC electric power bus subsections wherein each DCelectric power bus subsection includes first and second bus tie breakersfor selectively connecting and disconnecting the DC electric power bussubsection to the DC electric power bus. In some embodiments, theplurality of AC electric power bus subsections are electricallyconnected to the AC electric power bus in a ring configuration; and/orthe plurality of DC electric power bus subsections are electricallyconnected to the DC electric power bus in a ring configuration. One orseveral AC combustion generator(s) may be directly connected to each ofthe plurality of connectable AC electric power bus subsections. One orseveral kinetic generators 108 may be directly connected to each of theplurality of connectable DC electric power bus subsections. Each ACelectric power bus subsection may be energized by the one or morekinetic generators 108 even under system operating conditions where theAC combustion generator of the AC electric power bus subsection inquestion fails and the AC electric power bus section is isolated by thefirst and second bus tie breakers.

Certain embodiments of the featured systems and methods of the presentdisclosure may be used in, for example, various types of drilling rigssuch as drillship, semi-submersible rig, jack-up rig, barge or landrig,etc. However, the present systems and methods are not limited todrilling rig applications. For example, the featured microgrid electricpower generation systems could be used in other marine vessels, such ascommercial and military ships. The disclosed microgrid electric powergeneration systems may be particularly beneficial in shippingapplications requiring minimal noise, heat, and pollution emissionsbecause kinetic generators 108 are capable of providing electric powerwith significantly less heat and noise compared to combustiongenerators. Additionally, kinetic generators 108 emit essentially nopollution during operation, in contrast to combustion generators whichtypically emit significant pollution during operation. Thus, thefeatured microgrid electric power generation systems may be particularuseful in shipping applications where ships spend significant time inharbor and in stealth military shipping applications. Other possibleapplications of the featured microgrid electric power generation systemsinclude uninterruptable power supply applications, subsea microgridelectric power generation systems, land-based microgrid electric powergeneration systems, and applications which require fast charging, suchas a hybrid ferry applications.

Changes may be made in the above systems and methods without departingfrom the scope hereof. For example, the electrical topologies of thefeatured systems and methods may be varied without departing from scopehereof. It should thus be noted that the matter contained in the abovedescription and shown in the accompanying drawings should be interpretedas illustrative and not in a limiting sense. The following claims areintended to cover generic and specific features described herein, aswell as all statements of the scope of the present method and system,which, as a matter of language, might be said to fall therebetween.

Additional Embodiments

(A1) A microgrid power generation system may include an AC or DC powerbus or plane and a first controllable ac combustion generatorelectrically connected to the AC or DC power bus for supply ofelectrical power thereto. The first controllable ac combustion generatorincludes a first data bus interface for receipt of first set-point datadefining power generation of the first controllable ac combustiongenerator. The microgrid power generation system further includes one ormore bus loads, such as a thruster drive, electrically connected to theAC or DC power bus. In addition, the microgrid power generation systemincludes a flywheel energy storage device electrically connected the ACor DC power bus, wherein said flywheel energy storage device includes asecond data bus interface for receipt of state control data forselectively causing the flywheel energy storage device to supply andabsorb/store electrical power from the AC or DC power bus. Furthermore,the microgrid power generation system includes a microgrid controllerconnected to the first controllable ac combustion generator and theflywheel energy storage device through the first and second data businterfaces, respectively, via a common data bus or several separate databusses. The microgrid controller further includes (a) a primary controlloop arranged to maintaining a predetermined voltage and/or frequency onthe AC or DC power bus by adaptively adjusting power delivery and powerabsorption of the flywheel energy storage, and (b) a secondary controlloop arranged to adaptively adjusting supply of electrical power to theAC or DC power bus by increasing or decreasing power generation of thefirst controllable ac combustion generator in accordance with at leastone control variable.

(A2) In the microgrid power generation system denoted as (A1), thesecondary control loop may be configured to adjust a first set-point ofthe first controllable ac combustion generator to increase or decreaseits power generation, and/or the secondary control loop may beconfigured to deactivate and activate the first controllable accombustion generator to increase or decrease its power generation.

(A3) In either one of the microgrid power generation systems denoted as(A1) and (A2), the least one control variable of the secondary controlloop may include one or more of (a) a current amount of energy stored inthe flywheel energy storage device, (b) an energy or power dischargerate of the flywheel energy storage device, and (c) a current or averagepower consumption of the one or more bus loads.

(A4) In any one of the microgrid power generation systems denoted as(A1) through (A3), the primary control loop may include one or moreprimary control variables derived from a voltage and/or frequency on theAC power bus or a voltage on DC power bus.

(A5) In any one of the microgrid power generation systems denoted as(A1) through (A4), a time constant of the primary control loop may besmaller than 20 ms, preferably smaller than 10 ms, and/or a timeconstant of the secondary control loop may be larger than 100 ms,preferably smaller than 1 s.

(A6) In any one of the microgrid power generation systems denoted as(A1) through (A5), a peak load on the AC or DC power bus drawn by theone or more bus loads may be at least two times or three times largerthan a maximum power generation capacity of the first controllable accombustion generator.

(A7) In any one of the microgrid power generation systems denoted as(A1) through (A6), the microgrid controller may be configured to, (i)during an initialization phase/power-on phase of the microgrid, adjustthe first set-point of the first controllable ac combustion generator tosupply a total electrical power on the AC or DC power bus exceeding theelectrical power drawn or consumed by the one or more bus loads by asurplus power amount, and (ii) controlling, via the common data bus, theflywheel energy storage device to absorbing and storing the surpluspower amount from the AC or DC power bus.

(A8) In the microgrid power generation system denoted as (A7), themicrogrid controller may be configured to (1) monitoring the charging orenergizing of the flywheel energy storage device caused by the storageof surplus power from the AC or DC power bus during the initializationphase/power-on phase, and (2) interrupting the storage of power in theflywheel energy storage device via the data bus when the energy reachesa predetermined charging criterion or limit.

(A9) In any one of the microgrid power generation systems denoted as(A1) through (A8), the microgrid controller may be configured to (I)repeatedly determining the current amount of energy stored in theflywheel energy storage device via the third data interface, (II)comparing the current amount of energy of the flywheel energy storagedevice with a predetermined energy limit, (III) if the current amount ofenergy falls below the predetermined energy limit: increasing the firstset-point of the first controllable ac combustion generator, oractivating the first controllable ac combustion generator, to increasethe amount of power supplied to the AC or DC power bus, and (IV)controlling, via the common data bus, the flywheel energy storage deviceto retrieve and store energy from the AC or DC power bus.

(A10) Any one of the microgrid power generation systems denoted as (A1)through (A9) may further include one or more additional controllable accombustion generator(s) each electrically connected the AC or DC powerbus for supply of electrical power thereto, wherein each of the one ormore additional controllable ac combustion generator(s) includes a databus interface for receipt of respective set-point data from themicrogrid controller via the common data bus, and wherein the respectiveset-point data are defining power generation of the one or moreadditional controllable ac combustion generators.

(A12) Any one the microgrid power generation systems denoted as (A1)through (A10) may further include one or more additional flywheel energystorage device(s) electrically connected the AC or DC power bus, whereineach additional flywheel energy storage device includes a data businterface for receipt of state control data for selectively causing theflywheel energy storage device to supply and absorb/store electricalpower from the AC or DC power bus.

What is claimed is:
 1. A method for operating a microgrid electric powergeneration system, comprising: delivering energy to a first electricpower bus at least partially from one or more kinetic generatorselectrically coupled to the first electric power bus, the one or morekinetic generators storing energy therein in kinetic form; controllingthe one or more kinetic generators in response to a change in a loadpowered by the first electric power bus such that a magnitude of avoltage on the first electric power bus remains within a predeterminedvoltage range, while maintaining an output power of one or morecombustion generators electrically coupled to the first electric powerbus at a constant value during the change in load; and controlling theone or more combustion generators based at least in part on an operatingstate of the microgrid electric power generation system.
 2. The methodof claim 1, further comprising controlling the one or more combustiongenerators independent of the voltage on the first electric power bus.3. The method of claim 1, wherein a magnitude of the change in load isat least ten percent of a magnitude of the load before the change inload.
 4. The method of claim 3, wherein a duration of the change in loadis at least one second.
 5. The method of claim 1, wherein the one ofmore kinetic generators are electrically coupled to the first electricpower bus via at least one of a power converter and a transformer. 6.The method of claim 5, wherein the one of more kinetic generators areelectrically coupled to the first electric power bus via a secondelectric power bus.
 7. The method of claim 1, further comprisingmaintaining the output power of the one or more combustion generators ateighty percent or more of a maximum rated output power of the one ormore combustion generators during the change in load.
 8. The method ofclaim 1, further comprising controlling the one or more combustiongenerators in response to a signal indicating an upcoming change in theload.
 9. The method of claim 1, wherein controlling the one or morecombustion generators based at least in part on the operating state ofthe microgrid electric power generation system comprises controlling theone or more combustion generators according to one or more of (a)kinetic energy storage level of the one or more kinetic generators and(b) kinetic energy loss rate of the one or more kinetic generators. 10.The method of claim 1, further comprising: controlling the one or morekinetic generators in response to the change in the load within 10 ms ofthe change in load; and controlling the one or more combustiongenerators at least one second after the change in load.
 11. The methodof claim 10, the step of controlling the one or more combustiongenerators comprising: initiating change in operation of the one or morecombustion generators; and changing power output of the one or morecombustion generators at least one second after the step of initiating.12. The method of claim 1, further comprising providing an output powerof at least 1 MW from the one or more kinetic generators to the load forat least 5 minutes.
 13. The method of claim 1, further comprisingspinning a rotor of each kinetic generator at a speed of at least 30,000revolutions per minute.
 14. The method of claim 1, wherein the firstelectric power bus is an AC electric power bus and the method furthercomprises controlling the one or more kinetic generators such thatfrequency of the voltage on the first electric power bus remains withina predetermined frequency range.